1. Field of the Invention
The present invention relates to a recording disc and a method for playback of the data recording disc, and in particular to a recording disc (referred to hereinafter simply as a disc) having index codes recorded repetitively in lead-in area thereof and its playback method.
2. Description of Background Information
Small-diameter audio discs having a diameter of approximately 12 cm and having digital signals recorded thereon, generally called "compact discs" or CDs, are now well known. However, in recent years another type of disc, referred to in the following as a composite disc, has been developed, having an area in which is recorded an FM modulated video signal with a PCM signal superimposed thereon, as well as an area having only a PCM signal recorded.
With such a composite disc, the area having only PCM data recorded, e.g. audio data in PCM form, may for example be disposed in an inner peripheral area of the disc, (this area being referred to hereinafter as the CD area), while the area containing the FM video signal with superimposed PCM signal (this area being referred to hereinafter as the video area) may be disposed peripherally outward from the CD area, separated therefrom by a predetermined radial distance.
Furthermore, with a compact disc, index codes which relate to the recorded contents are provided in the lead-in area, thus enabling special playback operations such as the program search operation or the program skip operation. The index codes indicate such information as the number of recorded programs (or tracks), total playback time, and playback time of each track. When the playing of the disc starts, the information recorded in the lead-in area is read out before the playback of the information of each track begins. Therefore, also in the composite disc, the index codes are to be recorded in the lead-in area so that special playback mode operations becomes possible.
However, with the composite disc, the recording area is divided into two areas, and a lead-in area is provided for each of the two recording areas. Therefore, different two sorts of index codes should be provided correspondingly to two recording areas which carry different sort of information. With respect to such two sorts of index codes, each sort of index code has to be recorded, as well as in the corresponding recording area, in the other recording area so that any of the special playback mode operations can be performed throughout the different two recording areas. In recording these two sorts of index codes in the same lead-in area, it is desirable to adopt a recording method which is sufficiently efficient in view of various playback operations. Furthermore, in determining the playing method for playing a recording disc on which two sorts of index codes are recorded mixedly in a single lead-in area, it is desirable that the efficiency of the playback operation will not be negatively affected by the necessity for reading different two sorts of index codes recorded on the recording disc.